Embodiments described herein generally relate to a tubular linear electric motors, especially such motors in which a relatively long stroke and high linear motive force are desired, such as for use with downhole pumps in wells. The present invention relates to a cost effective modular design and method of constructing long stators having multiple sets of coils for use in applications requiring a rugged and reliable design. In certain embodiments, the stator is made by assembling a multiplicity of identical modules which are combined to form a stator of whatever length may be required. In some embodiments, coil modules containing the coils are connected by intermediate connectors. In those embodiments, the sum of the effective length of the coil module and the effective length of the intermediate connector must be an integral multiple of the pole pitch of the magnets in the motor's mover.
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. A linear electric motor is an electric motor which produces a linear force along its length. The more common electric motor has a stator, which remains stationary, and a rotor, which rotates and produces a torque. Instead of rotating like the standard electric motor, a linear motor has a stator and a mover which reciprocates along the longitudinal axis of the stator. A tubular electric linear motor typically has a cylindrical housing enclosing a series of ring-shaped coils for generating a variable magnetic field in the hole in the center of the rings. The coils are aligned perpendicularly along a common axis so that the holes through the middle of the coils form a cylindrical passageway along the axis of the stator. The cylindrical mover typically carries an array of permanent magnets on its surface and reciprocates in the passageway along the axis of the stator.
In some linear motors, the roles of the stator and mover are reversed—a cylindrical rod carrying elements which generate a magnetic field is fixed on one or more supports, and an annular element containing axially aligned coils encircles the rod and moves back and forth along the length of the rod.
Linear motors offer potential advantages over other reciprocating machines because of their mechanical simplicity and relatively low friction between the stator and the mover.
Examples of tubular electric linear motors can be found in U.S. Pat. No. 5,276,293 to Narumi et al., U.S. Pat. No. 5,298,819 to Suganuma et al., and U.S. Pat. No. 5,365,131 to Naito et al.